1. Field of the Invention
The present invention relates to a balancing system for an engine, and more particularly to a housing adapted to be disposed within an oil pan for accommodating balance shafts, balance shafts for the balancing system which are each provided with a counterweight portion, and an engine oil return passage provided in the engine comprising below a crankshaft, a housing for accommodating rotatably therein balance shafts.
2. Description of the Related Art
A balancing system is publicly known in, for example, JP-A-2001-74104 in which balance shafts are disposed below a crankshaft in an oil pan, so that the rotation of the crankshaft is transferred to the balance shafts via a chain/sprocket mechanism or gear mechanism.
Because the balance shafts in the balancing system are provided below an oil level within the oil pan, the balance shafts are entirely covered with a housing in order to eliminate any inconveniences that would be caused by the agitation of oil by the balance shafts. In addition, because a large amount of oil remaining within the housing constitutes rotational resistance against the balance shafts, oil remaining within the housing must be discharged as soon as possible, and the above Japanese Unexamined Patent Publication discloses a construction in which oil within the housing is discharged by the rotating balance shafts.
In the prior art construction, however, because the oil discharge ports are constituted by slits formed in the joint surface between the upper and lower housing, the slits are submerged below the oil level. Therefore, when this construction is adopted in an engine which is installed such that axes of cylinders are inclined relative to an orientation which is normal to an axis of the crankshaft, it is conceivable that oil flows back into the housing.
In order to secure the designed amount of oil to be discharged with the oil discharge ports being provided at positions that are not submerged below the oil level or in the upper housing, the area of the discharge ports has to be increased. However, such a construction tends to reduce the rigidity of the upper housing.
Further, a balancing system is disclosed in JP-B-3-18761U in which balance shafts each provided with a counterweight portion are disposed below a crankshaft.
With the balance shafts disclosed in the Japanese Examined Utility Model Publication, thrust supporting faces provided at a journal portion of each of the balance shafts for restricting axial movements of the balance shaft are designed to slidably contact with end faces of an opening in a bearing hole. In addition, it is known that thrust supporting faces are integrally formed on the balance shafts in order to reduce the number of components.
Incidentally, because the thrust supporting faces integrally formed on the journal portion are naturally provided with a larger diameter than that of the journal portion, according to the above construction, irrespective of the position of the weight, a part of the thrust supporting face situated on the opposite side of the balance shaft to the side thereof where the weight is provided becomes like a flange, and an outer circumferential side of the part comes to have a cantilever-like construction. Thus, the rigidity of the thrust supporting face at the part tended to be insufficient.
Moreover, while engine oil which has been used to lubricate and cool a valve train provided on a cylinder head is returned to an oil pan via a return passage provided in a cylinder block or the like, it is preferable that return oil is prevented from contacting the crankshaft which rotates at high speed within a crankcase in order that atomized oil is not mixed in blow-by gas.
There are known as a method for this purpose a construction in which a pipe extending to below an oil level in the oil pan is connected to a downstream end of a return passage provided in a cylinder block and a construction in which a return passage extending to the vicinity of an oil level is provided in a crankcase (JP-A-61-113910U).
According to the conventional constructions, with the construction utilizing the pipe, because the pipe comprising a separate member is required, the number of components is increased, and moreover, the number of man hours for mounting the pipe is also increased. In addition, with the construction is which the return passage is provided in the crankcase, because a mold for the crankcase becomes complicated, and it is difficult to provide the oil discharge port at a position where the oil discharge port is always allowed to be submerged below the oil level irrespective of a change in vehicle posture or driving condition.
The present invention has been made to solve the problems inherent in the prior art.
A first object of the present invention is to provide a housing for balance shafts which can restrain the decrease in rigidity of the upper housing while securing the area of the oil discharge ports and which is improved such that oil is difficult to contact the balance shaft.
A second object of the present invention is to provide balance shafts for a balancing system for an engine which are improved so as to increase the rigidity of the flange-like thrust supporting faces.
A third object of the present invention is to provide balance shafts for a balancing system for an engine which are improved so as to suppress an increase in weight resulting from reinforcement to a minimum level.
A fourth object of the present invention is to provide an engine oil return passage which is constructed to be formed without calling for increases in the number of components and the number of man hours required for production.
In addition, a fifth object of the present invention is to provide an engine oil return passage which is constructed such that an oil discharge port can be provided at a position which is not affected by changes in vehicle posture and driving condition.
With a view to attaining the above objects, according to a first aspect of the present invention, a housing (14U, 14L) for balance shafts adapted to be disposed within an oil pan (5) for accommodating therein balance (13L, 13R) shafts comprises an upper housing (14U) and a lower housing (14L) which are divided vertically along a plane parallel to axes of the balance shafts, and oil discharge ports (44a, 44b) and vertical walls (47) are provided on the upper housing which vertical walls (47) are provided so as to extend from portions at inner edge portions of the oil discharge ports which extend in parallel with the axis of the balance shaft toward a joint surface thereof with the lower housing.
According to the construction, not only can the decrease in rigidity of the upper housing be restrained while securing the area of the oil discharge ports but also the contact of oil flowing in from the oil discharge ports to the balance shafts can be restrained by the vertical walls. Thus, this results in no increase in rotational resistance.
According to a second aspect of the present invention, the vertical walls extend to reach the joint surface with the lower housing.
According to the construction, not only can the decrease in rigidity of the upper housing be restrained further but also the contact of the oil flowing in from the discharge oil ports to the balance shaft can be restrained further.
According to a third aspect of the present invention, there are provided within the housing two balance shafts which have different heights relative to an oil level and which are parallel to each other, the vertical walls are formed on a side of the upper housing where one of the balance shafts is disposed which is easier to contact oil flowing in from the oil discharge ports, and at least part of an oil inlet passage (a tubular passage 26) communicating from an oil strainer to an oil pump is provided in the lower housing on a side thereof where the other of the balance shafts is disposed in a manner so as to extend in parallel with the axis of the balance shaft.
According to the construction, not only can the rigidity of the upper housing on the side thereof where the one of the balance shafts is disposed be increased to thereby increase the supporting rigidity of the one of the balance shafts but also the contact of oil flowing in from the oil discharge ports to the one of the balance shafts can be prevented. In addition, the rigidity of the lower shaft on the side thereof where the other of the balance shafts is disposed can be increased by the oil inlet passage to thereby increase the supporting rigidity of the other balance shaft.
According to a fourth aspect of the present invention, ribs (46) are formed on an upper face of the upper housing which are parallel to the axis of the balance shaft and which connect, respectively, to the vertical walls.
According to the construction, the rigidity of the upper housing can be largely increased to thereby increase further the supporting stability of the balance shaft, and at the same time oil remaining on the upper surface of the upper housing can be restrained from entering the interior of the housing from the oil discharge ports.
According to a fifth aspect of the present invention, there are provided balance shafts (13L, 13R) for a balancing system (4) for an engine each having flange-like thrust supporting faces (19) which are integrally formed on a journal portion (16c) for restricting axial movements of a counterweight portion (17) and which each have a larger diameter than that of the journal portion, the balance shafts each having ribs (21) connected, respectively, to backs of the flange-like thrust supporting faces and extending in an axial direction on an opposite side to a side where the counterweight portion is provided.
According to the construction, because the rigidity of the flange-like thrust supporting faces in a radial direction can be increased, a highly accurate thrust control can be implemented. In addition, because the ribs are connected, respectively, to the backs of the thrust supporting faces and are caused to extend in the axial direction, an increase in weight on the side opposite the side where the counterweight portion is provided can be suppressed.
In addition, according to a sixth aspect of the present invention, in a construction as set forth in the fifth aspect of the present invention, the journal portion is provided at an axially central portion of the counterweight portion, and the flange-like thrust supporting faces are integrally formed at axial ends of the journal portion. According to the construction, because the rigidity of the journal portion to which a largest load is applied can be increased, the stable support of the balance shafts can be attained. In addition, in a case where lubricating oil is supplied to the journal portion, because lubricating oil is held by the flange-like thrust supporting faces, the lubricating effect on the journal portion is improved.
Furthermore, according to a seventh aspect of the present invention, the ribs are constructed to connect the two journal portions situated at the axial ends of the counterweight portion. According to the construction, because the rigidity between the journal portions can be increased, the diameter of a shaft portion can be reduced while obtaining a desired rotational mass to thereby suppress an increase in weight.
According to an eighth aspect of the present invention, in addition to a construction as set forth in the seventh aspect of the present invention, the height of the rib is constructed to be gradually reduced so that there is provided a valley at an axially intermediate portion of the rib. According to the construction, the stress distribution can be normalized to thereby suppress further the increase in weight.
According to a ninth aspect of the present invention, part (a downstream portion 142) of an engine oil return passage for returning engine oil from a cylinder head side to an oil pan (5) is provided in a housing (14U, 14L) provided below a crankshaft (1) for accommodating rotatably therein balance shafts (13L, 13R).
According to the construction, it is possible to form the engine oil return passage which opens below the oil level in the oil pan without calling for increases in the number of components of the engine itself and the number of man hours required for production.
According to a tenth aspect of the present invention, the housing comprises an upper housing and a lower housing which are divided vertically, and part (grooves 42b, 42c) of the return passage is formed in a joint surface between both the housings.
According to the construction, the passage can be laid out relatively easily so that the oil discharge port can be positioned at an optional position, and moreover, since the momentum of return oil can be reduced, engine oil within the oil pan is allowed to be kept unstirred.
According to an eleventh aspect of the present invention, an oil discharge port (143) of the return passage opens at a position adjacent to a suction port (29) of an oil strainer (25) provided on a bottom of the housing.
According to the construction, it is possible to provide the oil discharge port at the position where the oil discharge port is allowed to be always submerged below the oil level irrespective of a change in vehicle posture or driving condition.
In particular, according to a construction in which a portion (a tubular portion 144) where the oil discharge port opens is directly connected to an oil strainer mounting portion (28) which is integrally formed on the bottom of the housing (a twelfth aspect of the invention), can the oil discharge port be free from being affected by changes in vehicle posture and driving condition, but also the rigidity of the portion where the oil discharge port opens can be increased.